Fluidized selective adsorption separation process



Apnl 28, 1953 .1. H. wlDDows-ON Er AL 2,635,574

yFLUIDIZED SELECTIVE AnsoRPTIoN` SEPARATION PROCESSv Filed Dec. 21, 1950 mZON ZOChOw INVENTORS J. H. w|ooowsoN H. R. sAlLoRs A TTORNEVS Patented pr. 28, 1953 FLUIDIZED SELECTIVE ADSORPTION SEPARATION PROCESS John H. Widdowson and Howard R. Sailors, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Appui-.anon December 21, 1950,' serial No. 202,002

Claims.

This invention relates to selective adsorption. In a more specific aspect it relates to separation of gaseous mixtures utilizing a selective adsorbent in uidized state. In a still more specific aspect, this invention relates to the separation of natural and/or refinery residue gases utilizing fluidized` selective adsorbents.

It is known in the art that gaseous mixtures can be separated utilizing fluidized selective adsorbents. However, the iiuidized processes of the prior art do not satisfactorily provide a means for separating gaseous mixtures into three or more fractions. Prior art processes teach the separation of a gaseous mixture into two fractions and require doubling the separation equipment if the gaseous mixture is separatedinto three fractions, that is, an overhead fraction, an intermediate fraction and a bottoms fraction. The process of our invention is an improvement over prior art processes, since we provide a process which can be operated to produce one or more side-cut fractions, which is easy and economical to operate and which uses a relatively small amount of equipment, thus cutting down capital expenditure.

In the process of our invention wherein one side-cut fraction is produced, a gaseous mixture comprising material of intermediate adsorbablity, a less readily adsorbed material and a more readily adsorbed material is passed into a first section of an adsorption zone wherein a nely divided solid selective adsorbent is suspended in said gaseous mixture. In this first ysection the more readily adsorbed material is adsorbed by the solid selective adsorbent. The resulting adsorbent is withdrawn from the first section of the adsorption zone and the adsorbate is stripped from the adsorbent in a stripping zone. Resulting stripped adsorbent is cooled and recycled to the first section of the adsorption zone to be used for further adsorption. A finely divided solid selective adsorbent having a particle size smaller than that rof the adsorbent employed in the first adsorption operation is suspended in unadsorbed gases resulting from said first adsorption operation in a second section of the adsorption zone, and the material of intermediate adsorbability is adsorbed by this select-ive adsorbent. The resulting adsorbent from this second adsorption operation is removed from the adsorption zone, and the adsorbate is stripped from the adsorbent in a second desorption zone. The resulting stripped adsorbent is cooled and recycled to the second section of the adsorption zone for further use in adsorb- 4ing material of intermediate'adsorbability.` Less readily adsorbed material in the gaseous mixture Which is unadsorbed is removed from the second section of the adsorption zone. If the gaseous mixture contains twocomponents of intermediate adsorbability, the gaseous mixture can be separated into four fractions by usingan adsorption zone with three sections and selective adsorbents of three sizes. By the use of our process as many fraction-s can be produced as are desired, providing fractions or components are of ldiierent adsorbability.

It is an object of this invention to provide a process for carrying on selective adsorption separation.

It is another object of our invention to provide a process for separating a gaseous mixture into three or morefractions by the use of iiuidized absorbente.

Still another object of our` invention is to provide a process for treating natural and/ or renery residue gases to separate same into three or more fractions by the use of fluidized selective adsorbents. Y y Y Other objects and advantages of the process of our invention Will become apparent toA one skilled in the art upon reading this disclosure.

In the' drawings which accompany and are a part of this disclosure, Figure 1 is a schematic flow sheet showing a preferred method of carrying on our process to separate a gaseous mixture into three fractions,` that is; an overhead fraction, a side-cut fraction and a bottoms fraction. Two vstripping zonesV are used in conjunctionwith an adsorption'zone-having two sections. Figure 2 of the drawings schematically shows another method of stripping the selective adsorbent which has-been removed from' each of the sections of the adsorption zone.

.The vprocess of our invention can be usedto separate a gaseous mixture comprising a material of intermediate adsorbability, a less readily adsorbed material and a more `readily adsorbed material into three fractions. A gaseous mixture can be separated into as many fractions as there-are components inthe feed vgas of different adsorbabilities by the'use of enough sections in the adsorption zone and fluidized adsorbents'of enough differentpsizes Throughout the petroleum and natural gas industries as well as-the chemical industries, hydrocarbon streams comprising C1 to C4 and other low-boiling normallyl gaseous materials are available; AIn the case of natural gas residuelstreams, these hydrocarbon materials are usually saturated, while in thecase of refinery residue streams, thesehydrocarbons are usually a mixture of saturated and unsaturated compounds,

In either case our process can be utilized to separate these gas streams into their components as desired. These streams will also contain nitrogen and hydrogen. rline process oi our invention is particularly valuable in treating these streams to produce a C2 concentrate and a C3 concentrate for conversion processes, such as conversion to ethylene to be used in the synthesis of chemicals or valuable fuels. Another particularly valuable separation which can be made by using the process of our invention is the treatment of a natural and/or refinery residue gas to separate and recover a Cz stream and a Ca-Ci stream to be used or marketed as LPG. The separation and recovery oi ethylene from the low-boiling normally gaseous materials and eiiluent resulting from the pyrolysis of low-boiling normally gaseous saturated hydrocarbons canbe accomplished by the process of our invention. Such materials usually comprise methane, ethane, ethylene, propane, propylene, butanes and butylenes. If the stream contains methane and C2 and C3 hydrocarbons, it ycan be separated into a methane stream, an ethane stream, an ethylene stream, and a C3 hydrocarbon stream. Butanes and butylenes can be handled in our process and can be separated and recovered along with the C3 hydrocarbons or they can be produced as a C4 hydrocarbon stream. Many other separations can be made using the process and apparatus of our invention as will be apparent to one skilled in the art.

The process of our invention is best understood from the following description with reference to accompanying Figures l and 2 of the dra-wings. Figure 1 schematically sets forth the process whereby a mixture of gases, for example, a gas comprising methane, ethane and propane can be separated into an overhead stream of methane, a side-cut of ethane, and a bottoms fraction of .propane. It is to be understood that the following discussion is not t0 unduly limit the scope of our invention.

Referring now to Figure l, the feed gas stream of methane, ethane and propane is vpassed via line d into the lower portion of adsorption zone 6. Therein the feed gas is directly contacted with a finely divided selective adsorbent, such as activated charcoal, silica gel, etc., passed into the lower section of adsorption zone 6 via line 8. The velocity of the feed gas stream through the lower section and the size of the selective adsorbent particles are such that contact occurs while the silica adsorbent is in a uidized state, that is, the selective adsorbent is in suspension in the gas stream, is subject to top to bottom mixing and has a net downward velocity so that it can be removed, preferably from the lower portion of the lower section of adsorption zone 6. In operation, this selective adsorbent is not allowed to pass into the upper section of adsorption zone 6. However, due to a small amount of attrition which is encountered, small particles of adsorbent do pass into the upper section of adsorption zone 5, but as will be seen hereinafter, this causes no diculty since these small particles of adsorbent are utilized in the upper section of adsorption zone 6 to adsorb ethane.

'Contamination of adsorbent containing adsorbed Css with adsorbent containing Czs is prec vented because the adsorbent in the lower portion of zone 6 containing said adsorbed Cis will remain in said. lower portion due to the size of said vadsorbent relative to the size of the adsorbent in ,the upper portion of adsorbent zone 6. Disregarding the above-mentioned attrition, the par'- ticle size of the adsorbent is varied so that any particular part thereof will remain connected with one speciiic zone. The gas velocity will not be great enough to carry the particles in a lower zone up into a succeeding zone. The separation is not dependent upon particle size except for the fact that the use of different Yparticle sizes enables us to maintain distinct zones. The more readily adsorbed fraction is adsorbed in a first zone and, therefore, the second zone adsorbs the next more readily adsorbed fraction.

Selective adsorbent having propane adsorbed thereon is withdrawn from the lower section of adsorption zone i5 via line i0 and is passed into desorption Zone l2. In desorption zone I2, the .propane adsorbate is stripped from the selective adsorbent. Resulting propane is removed from desorption zone l2 via line Hl after entrained adsorbent is removed by separator IG which can conveniently be a cyclone separator, a lCottrell precipitator or a supersonic separator. This selective adsorbent, which has been removed `from the propane stream, is returned to the preferably luidized bed of selective adsorbent inthe lower portion of desorption zone i2. We have found it convenient to use a portion of the propane stream produced as the stripping gas with the remainder being produced as product withdrawn via line i8. The portion to be used as stripping gas is heated in exchanger 2] and passed into desorption zone i2 via line 22 wherein it is directly contacted with the selective adsorbent passed into desorption zone I2 via line I0. The propane is preferably stripped from the selective adsorbent while the adsorbent is in a luidized state, that is, subject to top to bottom mixing while in suspension and having a net downward velocity so that stripped adsorbent can be removed from the lower portion of the desorption zone.

Stripped adsorbent is removed from desorption Zone I2 via line 24 and passed back into the lower section of adsorption zone G Via lines 26 and 8 to be used for the further adsorption of propane. We nd it desirable to use a .portion of unadsorbed gases which have Abeen cooled to pick up and cool this adsorbent prior to its reintroduction into the adsorption section. This gas stream used to cool and transport 'the vse lective adsorbent is separated from selective adsorbent in separator -28 which can conveniently7 be a cyclone separator, Cottrell precipitator, or a supersonic separator. The resulting gases are withdrawn from separator 28 via line 30 and are either passed into line 32 or are combined with the overhead stream which is produced las hereinai ter set forth.

Unadsorbed gases are withdrawn 'from .the lower section of adsorption Zone G and are passed into an upper section of adsorption zone 6, which is, preferably enlarged as shown so that the gas velocity is reduced. The selective adsorbent oi smaller particle size than that used in the lower section of adsorption zone 6 is passed into the upper section via line 32. In this upper adsorption section this selective adsorbent and the unadsorbed gases resulting :from the adsorption in the lower section are directly contacted so that the selective adsorbent is Vin iluidized state, that is, subject to top and bottom mixing with a net downward velocity of the selective adsorbent so that it can be removed from the lower portion of this `.adsorption section. vIn the upper adsorption section, the ethane is adsorbed on the selective adsorbent.

Selective adsorbent is removed from the lower portion of the upper adsorption section of adsorption zone via line 34 and passed into desorption zone 36 wherein the ethane is removed from the selective adsorbent in preferably the same manner as that employed in stripping propane from the selective adsorbent in desorption zone l2. The selective ladsorbent is preferably sripped while in fluidized state with the ethane being produced via line 38. Here again, we nd that a portion of the ethane stream heated in exchanger 40 and passed into desorption zone 3d via line 42 can be advantageously used as the stripping medium.

Resulting stripped adsorbent is withdrawn from the lower portion ofdesorption zone 3B via line 44 and passed back into the upperportion of the upper section of adsorption zone 6 via line 32. A second portion of unadsorbed overhead -gas can very advantageously be cooled and used to cool and transport this selective adsorbent back into the adsorption section for further use in adsorbing ethane.

Unadsorbed gases are withdrawn from the upper portion of the upper section of adsorption zone 6 via line t6, after entrained selective adsorbent has been removed in separator ti8 which can conveniently be a cyclone separator, a Cottrell precipitator or a supersonic separator. This methane stream is withdrawn from the system via line 50. As set forth hereinbefore, a portion of this methane stream is passed via line 52 through exchanger Bil wherein it is cooled. The cooled methane stream is then used to cool and transport the selective adsorbents back into their respective adsorption sections of adsorption zone 6.

Figure 2 schematically shows another stripping method which we have found can be used advantageously in carrying on the process of our invention. Steam is used as the stripping gas and is passed into this desorption zone B via line 58. Heating coils 60 are employed to furnish heat to aid in stripping. Resulting stripped ethane or propane is removed in admixture with steam via line 62 and passed into exchanger 64 wherein the steam is condensed. Resulting ethane or propane and water are separated in separator 66, water being withdrawn via line 68 and the ethane or pi'opane being produced via line 10. Resulting stripped adsorbent is removed from adsorption zone 56 via line l2-and is passed back into adsorption zone 6 either into the upper -section or the lower section, as the case may be.

We find it desirable to use recording temperature controllers 14 and "I6 with temperature control points in the upper section and lower section of adsorption zone 6, respectively. The temperature in the fluidized bed indicates the particular adsorption which is taking place. For instance, if the temperature in the upper portion of the fluidized bed in the lower adsorption section gets too low, indicating ethane adsorption, the temperature controller will reduce the amount of adsorbent withdrawn via line l0, thus maintaining the adsorbent in the lower section 4for a longer period of time so that ethane will exit from the lower section and not be adsorbed 4to contaminate the propane product. Recording temperature controller 'M functions in the same manner to prevent methane from contaminating the ethane product, that is, if the temperature indicates vmethane adsorption in the 6. upper section of the fluidized bed, the rate of withdrawal of adsorbent via line 3d is reduced.

Differential pressure recording controllersy I8y and are utilized with desorption zones l2 and 36, respectively, to maintain the desired level of the iiuidized beds, that is, to maintain the interface between the relatively dense phase and relatively light phase Where desired. WhenA due to the recording temperature controllers Areducing the'A amount Aof absorbent. passed to the desorption zone, the differential pressure recording controllers reduce the amount of stripped adsorbent withdrawnfrom the desorption zone so that there is no excessive buildup in the adsorption sections of adsorption zone 6. We nd it desirable to use the same system whether a portion of the product gas is usedas a stripping medium or whethersteam is used as the stripping gas. As willbe apparent to one skilled in the art by increasing the number of adsorption sections in adsorption zone 0 Aand by increasing the number of desorption zones, a feed gas could be separated into more thanthree fractions. A `dif-y ferent particle size of selective adsorbent yis used in each adsorption section.

We have found that in the practice of our invention it is preferred to use an adsorbent of particle size 5 to 200 mesh, for instance, in the process wherein a feed mixture is separated into three fractions a particle size of from 5 to 40 mesh in the lower section and a particle size of 60 to 200 mesh in the upper section are preferred. The particle sizes of the adsorbent are dependent on each other and could be overlapping to a certain extent. Linear gas velocity is preferably in the range of 0.1 to 30 feet per second with a ratio of velocities of 2:1 to 10:1i lower to upper sections.

If the selective adsorbent becomes contaminated or poisoned during the operation of the process, we find that it can be reactivated for further use by stripping' same with superheated steam at a temperature of from 900 F. to 1200o F. in a separate reactivation zone or chamber (not shown on the drawings). The spent adsorbent is Withdrawn for reactivation via lines 82 and 84 after stripping in desorption zones l2 and 36, respectively. At reactivation temperatures of 900 F. to 1200 F. in the presence of steam, C5 and higher boiling hydrocarbons, absorption oils, resins formed from diolens, etc., can be removed from the adsorbent. It is desirable to remove C5 and higher boiling hydrocarbon materials from the feed steam prior to treating by the process of our invention. Mixtures of selective vadsorbents can be used to advantage in some separation operations, for instance, hydrophilic selective adsorbent, such as silica gel, can be used in conjunction with a hydrophobic selective adsorbent, such as many charcoal selective adsorbents, the hydrophilic adsorbent removing moisture and the hydrophobic adsorbent selectively adsorbing the other gases present. Also, selective absorbents, such as cuprous halides, can be used with selective adsorbents in some cases to separate mixtures containing unsaturated carbon atoms, such as oleiins, diolefins, carbon monoxide, etc. These cuprous halide absorbents, supported or unsupported, can be stripped, cooled and reactivated in much the same manner as the selective. adsorbents.

The preferred specific embodiment of the proc- 7 ess1of four 'invention,.:as set iiorth nereinbefora and 4Ithe @drawings -will :serve as .examples 4of the process-of zourginvention. However, such .preferredspecic 'embodiment ianddrawings are :not to unduly `limit the scopeofiour. invention.

As will be evident to those skilled :in :the art various--modiiica'tions -of .this 'invention .can be made, or lioll'owed,` lin the .light 'of this ldisclosure and discussion, 'without departing `from the spirit of vscope .of 'the .disclosure `:or from the scopeof-theclaims.

l. YA iprocess for separating -a :gaseous mixture comprising a .material .of .intermediate .adsorbability, 1a l:less readily .adsorbed material r'and a more aeadilyadsorb'ed material into three iii-ractions .which fcomprises: .suspending :a .fiinely'divided-'solid selective l.adsorbent infsaid .mixture a rst section of an adsorption zone under conditions such as .to eiectadsorption of said more readily yadsorbed material .a "First .adsorption operation; separating adsorbent resulting Vfrom said firstadsorption operation .andstripping same by heating isame; cooling resulting stripped .adsorbent and .recycling resulting icooled adsorbent to said rst section of said iadsorptionzcne; suspending Yianely divided solid selective adsorbent having 'a particlev size smaller than that ofsaid adsorbent employed in said first adsorption operation 'in unadsorbed rgases .resulting from said iirst adsorption operation ina second section of said adsorption zone under conditions such as t eiiect adsorption of said material vof intermediate adsorbability .in a second adsorption operation; separating-adsorbent resulting from said second adsorption .oper-ation and `stripping same by heating saine; and cooling resulting stripped adsor ent and recycling resulting cooled adsorbent to saidsecond section of said adsorptionzone.

V`2. The process of claim 1 wherein said granular adsorbent employed in said' first and .second sec tions is Vactivated charcoal.

3. The process of claim 2 wherein gas velocity through said adsorption zone is Within a range of from v0.1 to 30 feet per second vwith a ratio of gas velocity in said rst sectionr to said second section ina range of rom2zl .to 19:1, said granular adsorbent `employed in said first section has a particlesize of from 5 'to 4'0 mesh and said granular adsorbent employed in said second section has a particle size otir'omr to 200 mesh.

2l. Aprocess for separating land recovering a C2 hydrocarbon fraction Vfrom 'a feed-gas mixture comprising methane, vC2 Vand KC3 hydrocarbons which comprises: introducing 'nely divided activated charcoal into a rst'sectioniof an 'adsorption zone, therein forming a iluidized-bed or same by directly contacting-saine with `said gas mixture passed into said iirstseetion -andadsorbing said Ca hydrocarbons on saidactvated charcoal; withdrawing resulting activated charcoal from said Vfirst `section and passing same into a first stripping zone,- therein .forming a nuidised -bed of same by directly contacting same with -a stripping gas passed into said first stripping zone, lheating said resulting .activated :charcoaland strippingA C3 .hydrocarbons fromesame; withdrawing resulting Ca hydrocarbons from said .first stripping zone, withdrawing .resultin'g stripped activated charcoal from .said i'irst Astripping :zone and Vcooling same byudirectly contacting same witha cooled gaseous stream .comprising unadsorbed .methane yproduced las :hereinafter set forth; separating resulting cooled activated charcoal from said stream of methane and :recyclingzisueh V-coolcd ,charcoal `to said first section 'of said absorption '.zon'e; intro ducing nely divided activated vcharcoallhaving lo particle size .smaller lthan .that of .said ractiv-amd charcoal employed in said first section of said adsorption .zone into a secondsection of said adsorption zone, therein forming a fluidized .bed of same .by directly contacting same with vunacisorb'ed gases 'resulting 'from said adsorption in said iirst -section and passed into said second section vand .adsorbing said'Cz hydrocarbons on said activated charcoal; withdrawing a stream comprising unadsorbed -methane from said second section; .withdrawing resulting activated charcoal from saidsecond section and ypassing same into a secondstripping zone, therein -forming a iiuidized bed of same by directly contacting same withxa stripping gas'passed .into said second'strippillg zone, heating 'said resulting vactivated fcharcoal and .stripping C2 hydrocarbons .from same; .Withdraw'ing 'resulting 1.62 hydrocarbons from Said second stripping zone; .witlfidrawing resulting stripped .activated :charcoal from said Second stripping zone .and :cooling same by directly Corltacting same with acooled gaseous stream comprising unadsorbed methane produced .as yhereinbeforeset forth; separating resulting cooled :activatcd charcoal from 'said `methane stream and lecycling Vsuch .cooled nharcoal to vsaid second Section of said adsorption zone.

l5. The .process of claim 4 wherein said feed'gas mixture valso `contains.nitrogen whichis removed .with vunadsorbed methane from said second section of said 'adsorptionzone .8. The process of claim 4 wherein said feed gas mixturealso contains C4 hydrocarbons which are removed with IC3 hydrocarbons lfrom said first stripping zone.

7. The process of claim 4 :wherein .said .feed gas mixture comprises hydrogen, methane, ethane, ethylene, propane and propylene v8. 'lhe process of claim .e wherein gas velocity vthrough said adsorption zone ,is Within .a range of from 0.1 `150.3() feet per second with a `ratio .of gas velocity in said `first section to .said second section in a .range :of from l2:1 to 10:1, said iactivated charcoal employed in said first `section has a particle size of from 5 to l0 mesh, said activated charcoal employedin said second sec- .tion lhas a `particle size of from 60 to 200...mesh and said strippingg-as .passed into said first and second stripping .zones vis steam.

9. A ,process tor separating a gaseous .mixture comprising materials of varying Iabsorbabili'ty comprising: successively -introducing a .gaseous mixture into a `series of Aadsorption .zones .containing a finely divided suspended solid .selective .adsorbent under Aconditions .such as .Ito AeiTect-adsorption of the most `readily adsorbed component of the mixture in each said zone in which each fsucceeding vadsorbent `zone .operates with successively smaller particle size ladsorbents; removing yadsorbent resulting trom said .adsorptioncpera- .tion in each said zone .and separately stripping same .by heating; cooling resulting stripped adsorbent `and directly recycling resulting lcooled adsorbent to `ei/:ichsend '.zone.

Sl0.` n process for `separating a gaseous mixture comprising .materials `of `varying absorbability vwhich comprises: Ysuspending finely divided solid selective adsorbent Iinsaid mixture in a rst section of a .series of .adsorption zones containing at least .two .zones under conditions such Vas to eect adsorption of -a `preferentially adsorbed material; .separating .adsorbent resulting from said .rst adsorption operation; stripping the adsorbed gas from said absorbent by heating; cooling resulting stripped adsorbent and recycling said cooled adsorbent to said first section; passing gaseous effluent from said rst section of said series of adsorption zones through at least one o 10 recycling resulting cooled adsorbent to each said section of said additional adsorption zone.

JOHN I-I. WIDDOWSON. HOWARD R. SAILORS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,529,289 Gilliland 1 Nov. '1, 1950 2,539,005 Berg Jan. 23, 1951 2,548,192 Berg Apr. 10, 1951 2,548,502 Small Apr. l0, 1951 

1. A PROCESS FOR SEPARATING A GASEOUS MIXTURE COMPRISING A MATERIAL OF INTERMEDIATE ABSORBABILITY, A LESS READILY ADSORBED MATERIAL AND A MORE READILY ADSORBED MATERIAL INT O THREE FRACTIONS WHICH COMPRISES: SUSPENDING A FINELY DI- 